People often underestimate the power of... A small group of people. In Darfur, Congo, and northern Uganda, mini-movements are saying, "We are going to initiate change."

I felt most powerful when... My team helped negotiate peace between Ethiopia and Eritrea in 2000. After two years of war, we finally got them to sign a deal, and the guns literally went silent.

A true sign of power is... Humility. I've worked with President Mandela, and he has a way of being humbled by an issue, studying the problem, and then addressing it with endlessly fresh and innovative ideas.